Do I have to do something else to get the Palette to populate with widgets/controls?
</ End of Original Question

...and got this answer:

~~~~~~~~~~~~~~~~~~ ANSWER ~~~~~~~~~~~~~~~~~~~~~
What you are seeing is the expected behavior. Until you actually edit a UI class using WindowBuilder, those

views will be empty.

Also, this is not the correct place to ask WindowBuilder questions. Please use the WindowBuilder forum

instead.
</ End of Answer

So, I'm asking now: How do I "edit a UI class using WindowBuilder"?

I have an existing project that creates the GUI (buttons, edit boxes, etc.) in code, but I'd like to have the ability to move these controls/widgets around at design-time by dragging them so that my app is just plain instead of being 9X uglier than a bag of butts.